\documentclass[12pt]{article}
\usepackage{epsfig, amsmath}

\topmargin      0pt
\textheight     9.0in
\oddsidemargin  0pt
\evensidemargin \oddsidemargin
\marginparwidth 0.5in
\textwidth      6.5in

\begin{document}
\pagestyle{empty}

\title{Some graphs}
\maketitle

\begin{figure}
\begin{center}
\begin{minipage}{6.50in}
\centerline{
\epsfig{file=one.spring.center.eps, width=3.25in}
\hfill
\epsfig{file=one_hong.spring.center.eps, width=3.25in}
}
\hfill
\hfill
(a) Piecewise linear
\hfill
\hfill
\hfill
\hfill
(b) Hong
\hfill
\hfill
\hfill
\end{minipage}
\caption{}
\end{center}
\end{figure}

\begin{figure}
\begin{center}
\begin{minipage}{6.50in}
\centerline{
\epsfig{file=one.spring.corner.eps, width=3.25in}
\hfill
\epsfig{file=one_hong.spring.corner.eps, width=3.25in}
}
\hfill
\hfill
(a) Piecewise linear
\hfill
\hfill
\hfill
\hfill
(b) Hong
\hfill
\hfill
\hfill
\end{minipage}
\caption{}
\end{center}
\end{figure}

\begin{figure}
\begin{center}
\begin{minipage}{6.50in}
\centerline{
\epsfig{file=zero.spring.center.eps, width=3.25in}
\hfill
\epsfig{file=zero_hong.spring.center.eps, width=3.25in}
}
\hfill
\hfill
(a) Piecewise linear
\hfill
\hfill
\hfill
\hfill
(b) Hong
\hfill
\hfill
\hfill
\end{minipage}
\caption{}
\end{center}
\end{figure}

\begin{figure}
\begin{center}
\begin{minipage}{6.50in}
\centerline{
\epsfig{file=zero.spring.corner.eps, width=3.25in}
\hfill
\epsfig{file=zero_hong.spring.corner.eps, width=3.25in}
}
\hfill
\hfill
(a) Piecewise linear
\hfill
\hfill
\hfill
\hfill
(b) Hong
\hfill
\hfill
\hfill
\end{minipage}
\caption{}
\end{center}
\end{figure}

\end{document}
